package scw.retry;

/**
 * Interface for listener that can be used to add behaviour to a retry.
 * Implementations of {@link RetryOperations} can chose to issue callbacks to an
 * interceptor during the retry lifecycle.
 * 
 * @author shuchaowen
 *
 */
public interface RetryListener {
	/**
	 * Called before the first attempt in a retry. For instance, implementers
	 * can set up state that is needed by the policies in the
	 * {@link RetryOperations}. The whole retry can be vetoed by returning false
	 * from this method, in which case a {@link TerminatedRetryException} will
	 * be thrown.
	 * 
	 * @param <T>
	 *            the type of object returned by the callback
	 * @param context
	 *            the current {@link RetryContext}.
	 * @param callback
	 *            the current {@link RetryCallback}.
	 * @return true if the retry should proceed.
	 */
	<T, E extends Throwable> boolean open(RetryContext context,
			RetryCallback<T, E> callback);

	/**
	 * Called after the final attempt (successful or not). Allow the interceptor
	 * to clean up any resource it is holding before control returns to the
	 * retry caller.
	 * 
	 * @param context
	 *            the current {@link RetryContext}.
	 * @param callback
	 *            the current {@link RetryCallback}.
	 * @param throwable
	 *            the last exception that was thrown by the callback.
	 * @param <T>
	 *            the return value
	 */
	<T, E extends Throwable> void close(RetryContext context,
			RetryCallback<T, E> callback, Throwable throwable);

	/**
	 * Called after every unsuccessful attempt at a retry.
	 * 
	 * @param context
	 *            the current {@link RetryContext}.
	 * @param callback
	 *            the current {@link RetryCallback}.
	 * @param throwable
	 *            the last exception that was thrown by the callback.
	 * @param <E>
	 *            the exception to throw
	 */
	<T, E extends Throwable> void onError(RetryContext context,
			RetryCallback<T, E> callback, Throwable throwable);
}
